The present invention relates generally to sprayer assemblies, and more particularly to an airless application system with a tip cleaning function and a product container, and to a method of spraying using such a system.
Some aerosol products use a solvent to create a solution or suspension that includes the liquefied propellant. As environmental concerns have increased, aerosol products using water have become desirable. However, water does not mix easily with many propellant agents. In addition, film producing agents, such as adhesives, are designed with close tolerances with respect to miscibility and resistance to shear.
Most adhesives are made of synthetic polymers. In water-based adhesives, the polymer latex and resin dispersion constituents are suspended using surfactants. The surfactants have very specific functions within the system and are vulnerable to changes in temperature, shear, pH, and chemical contamination.
Adhesives are designed to create a film which is tacky and resistant to contaminants that may degrade the tacky characteristic. The film must not soften and release its hold on the substrate under varying conditions of exposure to heat, water, and solvents.
The same properties which are necessary in the adhesive are problematic in delivering the adhesive using an applicator. The surfaces of the application equipment, such as a spray gun, must remain free of adhesive build-up. If adhesive residue builds-up on the surfaces of the application equipment, the equipment may clog. The adhesive residue must then be removed manually by the user, which is time consuming and disruptive.
Most water-based adhesives are applied using air-assisted equipment. The application gun is designed with tandem valves so that both the air and product valves are open at the same time. The primary product is supplied to the gun from either a low-pressure container or through a venturi siphon and is atomized by a high-pressure stream of air. The compressed air helps keep the tip clean. However, air-assisted applicators are limited to locations where compressed air is available. In addition, they are prone to maintenance problems and the equipment can be difficult to adjust.
An airless solvent-based application system incorporates a needle valve to control the flow of the product to a tip designed to impart a particular pattern to the product as it exits the tip. In order to achieve this pattern, there is a space between the valve and the orifice. The space fills and swirls the product to obtain the spray pattern. When propellant is dissolved in the formula, the expansion in the tip space helps to clear the tip. However, for a simple-pressure pot system, there is no driving force to clear the tip when the valve is closed.
The use of water-based products in aerosol packages (that is, self-contained, pre-pressurized containers) is known. Formulations which require complete segregation from the propellants (such as “bag-in-can”) are also known. However, this technology has apparently not been used successfully for an adhesive and/or in a package larger than one liter.
Therefore, there is a need for an airless application system with a sprayer which can clear the sprayer tip after each application. There is also a need for an airless application system which uses a “bag-in-can” product container.